Hi all, I am new here. I require some advice on an accurate method of calculating Service Design Capability (The percentage that an IT Service is rated to comply too taking in to account its SLA and any underpinning component SLAs.

Currently we provide a capability assessment for our company of all our IT Services and the Design Capability figure is based upon the above but in a worst case scenario situation (no resiliency, all components treated as single points of failure) to get the design capability figure. We have discussed this and have decided that this worst case figure is so remote that it would literally be the end of the world for this to happen in which case it wouldn't matter anyway! But the decision has been made that we need a more accurate and realistic figure for IT Service Capability but I am struggling to find anything relating to it online or how other companies calculate this. It might be a stab in the dark and cant be achieved but any ideas you could throw out there to me about it would be really handy as im pulling my hair out trying to figure it out!

This is proactive availability management, you can find the parameters and risk calculation along with potential categories (single point of failure, design flaws, capacity issues, outdated firmwares etc) in the internet.

If you take this one step further it will be BIA (Business Impact Analysis) which will be base for your IT service continuity plan.